Chain Folding in Polyethylene and Cyclic Paraffins

With a view to a study of fold configurations, the crystal and molecular structure of a large cyclic paraffin (CH₂)₃₄ was determined by x‐ray diffraction. Three‐dimensional data were collected and the structure refined using a structure‐factor least‐squares computer program. The standard deviations in the final carbon atom coordinates were 0.02 Å. The configuration of the molecule was that of a ``collapsed'' ring, with two parallel linear chains linked by two terminal carbon atoms at either end. The chains packed together to give a triclinic subcell with dimensions $$\begin{array}{cc}\text{a=4.246\hspace{0.17em} Å}& {\text{α=60}}^{\circ }\text{30′}\\ \text{b=5.470\hspace{0.17em} Å}& {\text{β=74}}^{\circ }\text{08′}\\ \text{c=2.564\hspace{0.17em} Å}& {\text{γ=96}}^{\circ }\text{47′.}\end{array}$$ Restraints imposed by the fold configuration gave rise to a departure from optimum packing of the chains at some distance from the fold. A rough estimate of the surface free energy of polymer faces containing similar folds was made.